A torque sensing apparatus is used in a steering system having electrically controlled power assist to detect an applied input torque, i.e., steering torque. Such power assist steering systems include either an electric assist motor, an electrically driven pump, or an electrically controlled solenoid valve. Typically, the torque sensing apparatus is connected between an input shaft connected to a steering wheel and a pinion or output shaft. The detected torque is used to control an assist electric motor, an electrically driven pump, or a solenoid valve in response to a driver's input torque applied to a vehicle steering wheel.
One type of torque sensor for use in steering systems includes a Hall-effect position sensor, such as is disclosed in U.S. Pat. No. 4,415,054 to Drutchas, which is assigned to TRW, Inc. A magnet is positioned on one shaft adjacent and rotatable relative to the Hall-effect sensor on the other shaft. The Hall-effect sensor measures the relative rotation between the input and pinion shafts and, in turn, the amount of twist in a torsion bar operatively connected between the input shaft and the pinion shaft. The output voltage of the Hall-effect sensor varies as a function of the relative position of the magnet to the sensor and, in turn, the amount of applied steering or input torque.
Another type of torque sensor is disclosed in U.S. Pat. No. 5,442,956 to Persson, which is assigned to TRW Inc. This torque sensor includes a rotary input transformer having a stationery primary winding and a rotatable secondary winding. Relative rotation between the input shaft and the pinion shaft results in corresponding relative rotation between the primary and secondary windings. The windings provide an output signal that varies as a function of their relative rotational position, thus providing an indication of the applied input torque.
Another type of torque sensing apparatus is disclosed in U.S. Pat. No. 5,039,926. In this patent, each of a pair of sensor elements provides an output signal to a torque displacement converter. The output signals represent steering torque applied to a steering wheel. Each output signal is monitored so that, upon detecting a predetermined difference between the signals, a fail safe relay is activated to deenergize an electric steering assist motor.
U.S. Pat. No. 4,986,380 discloses a torque sensor that includes a right turn sensor element and a left turn sensor element that generate an associated output voltage signal corresponding to the steering torque during a right turn or left turn, respectively. A motor controller prevents the flow of motor current when both of the sensor elements generate an output voltage at the same time.
U.S. Pat. No. 4,598,787, which is assigned to TRW Inc., discloses a torque sensor that includes a sensor element having a resistive strip operatively connected with the pinion shaft and an arm associated with the input shaft. Upon applying a predetermined amount of steering force, the sensor element provides an output signal that varies as a function of the relative rotation between an input shaft and a pinion shaft.